This disclosure is directed primarily to heat pump systems which are applied to heating and air-conditioning loads of the environment in living spaces of buildings. As used herein the term air-conditioning means the adjustment of the temperature and humidity in the living space to selected comfortable norms when the outside environment, and particularly the ambient temperature, is either too high or too low for comfort. However many of the objectives and concepts of this invention also have application to other types of thermal loads. Therefore the term load as used herein while specifically in the context of air-conditioning, may be interpreted broadly to apply to other thermal loads by those familiar with heating and cooling technology.
It is well recognized that air-conditioning and heat pumping thermal systems require a fluid source to which the heat load may be transferred in the cooling mode and from which the heat may be transferred in the heating mode. In recent times and particularly in connection with air-conditioning activity, efforts have been directed to the convenient economical use of ambient outside air as the heat sink for the cooling load, and as the heat source in the heating or heat pumping mode.
When outside ambient air is used as a heat source in the heat pumping mode, and the ambient air is at low temperature, i.e., near, at, or below the freezing temperature of the moisture in the air, the problem of frozen condensate on the outdoor refrigerant heat exchanger is a serious one. As the moisture collects on the outside heat exchanger and builds up in the form of frost it acts as an insulator and reduces the heat exchange conductivity of the outdoor heat exchanger surfaces. With the reduction in conductivity there is the consequential reduction in thermal efficiency so that heat pumping effectiveness is drastically reduced.
This problem of frosting on the outdoor refrigerant coil, which is operating as an evaporator in the heat pumping mode, is well known and various means are provided in typical prior art systems to treat and overcome the problem. In most instances, the method of meeting this problem is to temporarily interrupt the heat pumping cycle long enough to reheat and defrost the surfaces of the heat exchanger. This is often done by the application of intense heat in the form of electrical resistance heaters and/or reversing the cycle to the heating mode so that the outdoor heat exchanger operates as a condenser for a short period of time. This solution to the problem reduces the overall coefficient of performance of the unit, since the use of input energy for other than heating the indoor space is counterproductive for the period when defrosting is taking place.
It has been recognized that when an internal combustion engine or other hydrocarbon burning prime mover is used to drive the compressor of a refrigerant vapor air-conditioning and heat pump system, all of the heat of burning the fuel is not used or applied to creating the motive power. The rejected energy in the form of heat is available for other purposes; one known use is to make domestic hot water. U.S. Pat. No. 4,697,434 Yayama discloses an air-conditioning and hot water supplying system capable of recovering heat discharged from the prime mover for utilization thereof as an auxiliary heat source for heating air as well a heat source for heating water to be stored in a hot water tank. In this patent, engine cooling fluid flows through a heat exchanger where it is selectively directed to heating hot water and/or boosting the thermal efficiency of the system by heat exchange with the refrigerant fluid.
Other patents in the prior art find other related uses and show the efforts made to take advantage of the "waste" engine heat.
U.S. Pat. No. 4,510,762 Richarts shows a heat recovery method of general interest.
U.S. Pat. No. 3,799,243 Castillo relates to liquid vapor cycle air conditioning systems of the reversible or heat pump type, i.e., systems which are capable of operating in both a heating and cooling mode. Waste heat from combustion is used in the process.
U.S. Pat. No. 3,421,339 Volk et al. shows an unidirectional heat pump system. Heat from the engine cooling is used in the heating cycle evaporator.
U.S. Pat. No. 3,135,318 Carleton reveals a heat pump system which has a turbine engine as its prime mover and makes use of the heat content of the exhaust of such engine so as to increase the efficiency of the system during both heating and cooling. The patent is of general interest to the concept of using waste heat in heat pumps.
These patents, while recognizing the advantages of using the waste heat, do not apply this heat to the outdoor heat exchanger in a total system including all of the components found in various teachings and constructions for gas-fueled engine driven refrigerant vapor fluid compressor heat pumping systems that include heating for utility hot water.